Effects of Salicylic Acid and Trichoderma harzianum on the Growth Parameters of Cucumber and its Reaction against Greenhouse Whitefly, Bemisia tabaci

Effects of Salicylic Acid and Trichoderma harzianum on the Growth Parameters of Cucumber and its Reaction against Greenhouse Whitefly, Bemisia tabaci GHADAH MAJID ABDULLAH ALGHANIMI1, ALIREZA JALALIZAND1*, YOUSIF DAKHEEL RASHID 2, ESMAEIL MAHMOUDI 1 1- Department of Plant Protection, Faculty of Agriculture, Water, Food and Nutraceuticals; Isf.C., Islamic Azad University, Isfahan, Iran 2- Al-Mussaib Technical Institue; Al-Furat Al-Awsat Technical University, Iraq. *Corresponding author’s E-mail: a.jalalizand@iau.ir Received: 8 November 2025 Accepted: 10 January 2026 ABSTRACT Plants are exposed to various threats, including insect pests and abiotic stresses, which can significantly reduce their growth and productivity. One of the key plant defense mechanisms is induced chemical defense, mediated through hormonal signaling pathways such as salicylic acid (SA) and jasmonic acid (JA), leading to systemic resistance against herbivorous pests. The present study was conducted to evaluate the effects of salicylic acid and the beneficial rhizospheric fungus, Trichoderma harzianum on growth parameters of greenhouse cucumber, reducing populations of the whitefly (Bemisia tabaci) and inducing systemic resistance against this pest. The experiment was carried out under greenhouse conditions using a completely randomized design with six treatments and four replicates. T. harzianum suspension were applied as soil inoculations, while different concentration of salicylic acid and humic acid were administered as a foliar spray. Pest population density and plant growth parameters were measured. The results demonstrated that all three treatments significantly reduced whitefly populations and enhanced plant defensive responses. T. harzianum not only directly suppressed pest populations but also activated induced systemic resistance (ISR). Salicylic acid enhanced resistance by increasing the activity of defense-related enzymes and the production of secondary metabolites. Humic acid improved plant nutritional status and growth, thereby indirectly strengthening plant resistance. These findings highlight that the application of biological and natural compounds such as T. harzianum, salicylic acid and humic acid can serve as a sustainable and effective strategy for greenhouse pest management and for reducing reliance on chemical insecticides.